The present invention relates to an apparatus for controlling an engine in accordance with engine operating conditions, and more particularly to an apparatus for controlling fuel injection quantity, ignition timing or the like in accordance with intake air flow quantity.
In an engine of an automobile, for instance, fuel injection quantity, ignition timing or the like is controlled by an electronic control unit (ECU) utilizing a micro-computer. In such electronic control unit, detection signals from sensors sensing engine operating conditions are applied to the control unit to be used therein for controlling the engine. For instance, the sensors sense respectively engine rotational speed, coolant temperature, throttle opening, air-fuel ratio and battery voltage of an engine. Further, intake air flow quantity which is most relevant to engine control, fuel injection quantity control, is sensed by an air flow sensor and detection signal thereof is applied to the control unit. As the air flow sensor for measuring intake air flow quantity used in engine control, various ones such as heat-wire type disclosed in U.S. Pat. No. 4,279,146 are known.
In the heat-wire type air flow sensor, a heater resistor having a specified temperature-resistance characteristic is provided in an intake passage of the engine so that the heating of the same is controlled by heating electric power supplied thereto. The temperature rising speed of the heater resistor supplied with the heating electric power is monitored. Since the heater resistor is exposed in the intake air flow, heat dissipation from the heater resistor corresponds to the intake air flow quantity. That is, if the intake air flow quantity increases, the temperature rising speed becomes slow. To keep the temperature condition of the heater resistor at a reference temperature, larger heating electric power is required as the intake air flow quantity increases.
In this type of air flow sensor, temperature condition of the heater resistor is sensed in relation to the temperature of air flowing through the intake passage sensed by a temperature sensitive resistor. However, in fact, the temperature measurement characteristic of the heater resistor is greatly influenced by the temperature of the environment. For instance, in a cold condition where the temperature is lowered to -20.degree. C., it becomes difficult to accurately measure intake air flow quantity. To compensate for dependency on the air temperature, a compensation resistor is connected to the temperature sensitive resistor. However, the compensation resistor only compensate for the temperature dependency linearly with respect to the sensed air temperature. This means that it becomes difficult to control the fuel injection quantity, ignition timing or the like precisely.